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CT Scans Deemed Best for Checking Heart Arteries
February 02, 2010
Start with a misleading headline and follow with a simple review of a complicated study of a complicated issue in medicine - a story that mischaracterizes the study's conclusions and its limitations.
Our Review Summary
The story misses the important context for this research: the investigators note that CT scans of the heart are only applicable in "selected patient populations." I
n both its introduction and conclusion, the
published study traces the boundaries for interpreting these results, e.g., "Coronary CT angiography is therefore best used in patients with a low to intermediate pretest likelihood of disease."
Thus the story's headline, "CT Scans Deemed Best for Checking Heart Arteries," is extremely misleading. The statements that sometimes doctors want to assess the heart's arteries without "putting a gadget in there," or that they "do not always want to run the risks" of catheterization imply that the study supports noninvasive testing as an alternative to invasive testing. It didn't. It compared two types of noninvasive testing to each other. It's important to note that the researchers did not claim CT is the "best" way to diagnose coronary artery disease, nor did they suggest that CT should replace catheterization.
Without commenting on the limitations of the study noted by the investigators, nor the costs and risks of CT scans, the story's general optimism makes it read like an advertisement for the technology rather than a balanced reporting of the findings of this research.
Why This Matters:
The oversights in this story are indeed unfortunate given the importance of coronary artery disease in the industrialized countries and its emerging importance in the developing world. It could add dubious fuel to the controversy, as described in a New York Times article, surrounding the evidence and expense related to CT scans of the heart.
Click on Criteria for definitions.
The story notes that CT and MRI are currently used in clinical practice. Both techniques are routinely available for imaging of the heart in most academic and large community hospitals.
The significant costs of both MRI and CT angiography are not discussed. Their adoption as screening tests could have a substantial impact on overall health care costs, and the omission of a discussion of costs is a major oversight. See this New York Times article for why the costs of CT angiography are relevant.
This story doesn't exaggerate the burden of coronary artery disease, the biggest cause of deaths for humans in the developed world.
It's worth nothing, however, that we think the story does exaggerate the number of people who are appropriate candidates for CT scans of the heart.
The story is clear about the type of study, that it was a meta-analysis or "review of studies." It also presents sensitivity rates and quotes outside sources noting that the conclusions were already known in general.
Now for the bad news. First, there is the misleading context, or lack of context, for this evidence, as we've described. We feel that the story, starting with its headline, is worded in such a general way that many readers will think the evidence supports the use of noninvasive over invasive imaging. Second, the story fails to report on specificity results, the percentage of healthy people who are correctly identified by the tests as not having the condition. See the Benefits criterion.
The story also does not note any of the limitations of the evidence acknowledged in the published study. These include:
- The review included very few studies of MRI (only 20 of the 109 studies)
- It included very few studies (only 5 of 109) that directly compared CT and MRI.
- There were some other methodological limitations.
Another part of evaluating the evidence is discussing what the review doesn't show, what we still don't know, and what future research is needed. The final sentence in the published study sums it up: "Randomized studies are clearly needed to address the potential of coronary CT angiography for use in triage as a means of positively altering management and outcomes in patients with suspected CAD [coronary artery disease]."
Although the story highlights the presumed advantages of CT scans, there isn't a single word about potential harms. That includes the radiation exposure leading to risks for cancer, which are acknowledges in the introduction to the published study. (According to the most recent estimates, the risks may be in the neighborhood of one case of cancer for every 800 individuals scanned.) The story also leaves out the specificity results of this research, ignoring the rates of false positives and their potential harms.
The story quotes an outside source as stating that "this article holds no surprises whatever," and that the underlying difference between CT and MRI were somewhat common knowledge already.
The story does provide some important details on the meta-analysis, including the number of studies and patients, as well as sensitivity results. However, we have two critiques:
1) It notes that the sensitivity results, 97% and 87%, were for the studies of people with suspected coronary artery disease. We believe that's incorrect. According to the published study, these figures are for the overall population in the meta-analysis, which includes those with suspected OR known disease, including those with heart attacks. For the analysis just of patients with suspected coronary artery disease, the results were different: 98% and 89%. But that's a minor problem. A bigger issue, to us, is the following.
2) We would have liked to have seen the specificity results, too. We're unsure why they choose to report just sensitivity and not specificity. False positives are important, too, besides just false negatives.
3) The study had clear limitations that were ignored in the story. The authors of the study concluded, "Randomized studies are clearly needed to address the potential of coronary CT angiography for use in triage as a means of positively altering management and outcomes in patients with suspected CAD (coronary artery disease)." The take home message for readers of this story may be that CT scans are "Best for Checking Heart Arteries" - as the headline states - a conclusion that has yet to be clearly demonstrated.
The story does not appear to rely on a news release.
The story does cite two independent sources who appeared unrelated to the study.
The story did not identify any potential conflicts of interest. While the study publication identifies no primary funding sources, the senior author, Marc Dewey, reports in his conflict of interest statement financial relationships with Toshiba Medical Devices, Bayer-Scherling, and Guerbet, companies that manufacture imaging devices or contrast media used with them. These relationships were disclosed by the medical journal when they published the study - yet the story makes no menton of them.
The story notes that CT and MRI are each used for different reasons, but it implies erroneously that either is an all-around alternative to catheterization, and thus the "best" way to detect coronary artery disease.
Total Score: 4 of 10 Satisfactory
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